Vehicles may use a brake booster in an internal combustion engine which uses vacuum to amplify driver braking force. As brake booster operation depends upon the pressure in a vacuum chamber of the brake booster, it may be important to diagnose whether the vacuum chamber evacuation and replenishment functionality is working properly.
In some systems, brake booster vacuum may be supplied by the intake manifold alone. Such systems may diagnose brake booster operation based on the relationship between sensed pressures in the intake manifold and the brake booster vacuum chamber, in some examples. However, the diagnostic methods employed in such systems may require brake actuation or detection of whether a braking cycle has occurred. Further, such systems may include physical models with integrators, and therefore may produce results that are highly dependent on the initial conditions (e.g., the initial measurement of pressure in the brake booster vacuum chamber).
In addition to recognizing the deficiencies of known methods for indicating degradation in brake booster operation noted above, the inventors herein have recognized that known methods may not be sufficient in some modern engines which include multiple distinct vacuum sources in addition to the intake manifold. For example, in some systems, brake booster vacuum may be supplied by one or more pumps such as vacuum pumps and flow powered pumps (e.g., ejectors/venturis/aspirators) in addition to the intake manifold. The inventors have identified that in such systems, brake booster vacuum may be dominated by the intake manifold when a higher vacuum level is present in the intake manifold than in the brake booster vacuum chamber. However, during conditions where a higher vacuum level is present in the brake booster vacuum chamber than in the intake manifold, the inventors have identified that brake booster vacuum may be dominated by the other vacuum sources. The inventors have recognized that the flow characteristics (e.g., mass flow rate) of many vacuum sources which commonly supplement intake manifold vacuum may be determined if the pressure differential across the ports is known. In addition, the inventors have recognized that such sources may be positioned within an engine system in such a way that existing pressure sensors may be used to measure the pressure differential across the source, which may then be used to determine the suction flow rate of the source.
As such, one example approach for diagnosing faults in brake booster operation in systems supplying brake booster vacuum via the intake manifold and one or more vacuum-powered pumps includes, when braking is suspended, indicating degradation based on expected BB vacuum, the expected BB vacuum based on expected mass air flow from the BB to the intake manifold when measured BB vacuum is less than intake manifold vacuum, and based on expected mass air flow from the BB to one or more vacuum-powered pumps when measured BB vacuum is not less than intake manifold vacuum. In this way, it may be possible to determine whether the brake booster is functioning properly even in systems where several active vacuum sources (e.g., ejectors/asprirators/venturis and driven pumps) are coupled with the brake booster in addition to the intake manifold. Specifically, by dividing brake booster behavior into two simplifying conditions, evacuation via intake manifold (e.g., when measured BB vacuum is less than intake manifold vacuum) and evacuation via vacuum-powered pump(s) (e.g., when measured BB vacuum is not less than intake manifold vacuum), brake booster degradation may be indicated even in systems which include a multitude of vacuum sources evacuating the brake booster. Advantageously, depending on the positioning of the vacuum-powered pump(s) within the system, existing engine sensors may be used to determine vacuum at inlets or suction ports of the pumps, and mass air flow at the pumps may then be determined using functional expressions stored in memory which relate mass air flow and vacuum for each pump. As a further simplification, brake booster fault diagnosis may also be performed during conditions where there is no vacuum consumption (e.g., when the vehicle operator's foot is off the brake pedal).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.